2023 Cambridge IGCSE Food and Nutrition (0648) 模拟试题及答案详解

(a) The deficiency disease of vitamin D in adults is osteomalacia (rickets occurs in children).
(b) Good dietary sources of vitamin D include fatty/oily fish (such as salmon or mackerel), eggs (especially the yolk), liver, butter, and fortified foods like margarine and breakfast cereals.
(c) Vitamin D acts as a regulator for calcium absorption in the gut. Without adequate vitamin D, the body cannot absorb calcium from the diet, leading to calcium being drawn from the bones, which weakens them.

(a) 1 mark for osteomalacia (reject rickets).
(b) 2 marks (1 mark per source) for any of: oily fish, egg yolk, liver, cod liver oil, fortified margarine/milk/cereals, butter.
(c) 2 marks (1 mark for stating that vitamin D is required for the absorption of calcium from the intestine, 1 mark for linking this absorption to the mineralization/strength of bones and teeth).

(a) Chemical digestion of carbohydrates begins in the mouth with salivary amylase (also known as ptyalin), which breaks down starch into maltose.
(b) Hydrochloric acid (HCl) is secreted by gastric glands. It serves vital functions: it creates an acidic environment (pH 1.5-2.0) necessary for pepsin to act, activates pepsinogen, halts the action of salivary amylase, and serves a protective role by destroying pathogens ingested with food.

(a) 2 marks (1 mark for salivary amylase / ptyalin; 1 mark for starch).
(b) 3 marks (1 mark per function) for any of: kills bacteria/pathogens; provides acidic environment/pH for stomach enzymes; activates pepsinogen/pepsin; denatures proteins to assist enzyme action; stops action of salivary amylase.

(a) Vitamin C is water-soluble, meaning any excess is not stored but excreted daily in urine, requiring constant dietary replacement. It acts as an antioxidant, is essential for synthesising collagen (connective tissue), and enhances the absorption of non-haem iron.
(b) While citrus fruits are famous for vitamin C, many other plants are highly concentrated sources, including strawberries, kiwi, red/green peppers, and cruciferous vegetables like broccoli and cabbage.

(a) 3 marks (1 mark per reason) for any of: water-soluble / cannot be stored; excess excreted in urine; required daily for collagen synthesis/wound healing; aids in absorption of non-haem iron; acts as an antioxidant.
(b) 2 marks (1 mark per correct source) for any of: strawberries, kiwi fruit, blackcurrants, green/red peppers, broccoli, cabbage, Brussels sprouts, tomatoes, spinach, potatoes. (Do not accept oranges, lemons, grapefruit, limes, or general 'citrus fruits').

When planning meals for preschool children, their physical and metabolic differences must be considered: they have small stomachs but high energy demands, so meals must be nutrient-dense but not overly bulky. Presentation (colours, shapes) encourages eating, while safety concerns require avoiding choking hazards. Developing kidneys and tastebuds require minimal salt, sugar, and strong spices.

5 marks (1 mark per distinct valid factor) for: portion sizes suited to small stomach capacity; colourful/attractive presentation (shapes, bite-size); easy-to-handle food/finger foods; nutritional balance (calcium/vitamin D for bones, protein for growth); avoid choking hazards (e.g., whole grapes, nuts); limit salt/sugar; texture variety; avoid strong spices/flavours; frequent small meals/snacks.

(a) NSP/dietary fibre absorbs water in the digestive tract, adding bulk to feces and stimulating peristalsis, which prevents constipation and reduces transit time, lowering bowel disease risks. It also promotes satiety and helps regulate blood sugar/cholesterol levels.
(b) To boost NSP in a fruit pie, modifications must target the pastry or crust: substituting refined white flour with wholemeal flour, or adding oats, bran, or seeds to a crumble crust.

(a) 3 marks (1 mark per benefit) for any of: stimulates peristalsis / prevents constipation; reduces transit time / lowers risk of colon cancer; adds bulk / promotes satiety (assists weight management); helps lower blood cholesterol; manages blood glucose levels.
(b) 2 marks (1 mark per distinct method) for: use wholemeal/whole-wheat flour in the pastry; add rolled oats to pastry or crumble topping; add seeds (e.g., flax, sesame, chia) to the pastry; add wheat bran to the flour mixture.

(a) A lack of iron leads to iron-deficiency anaemia, where hemoglobin levels are too low to transport oxygen efficiently.
(b) Common symptoms include chronic fatigue, pale skin (pallor), breathlessness due to low oxygen transport, and muscle weakness.
(c) Plant-derived iron (non-haem iron) is less easily absorbed than haem iron from meat. Its absorption is dramatically improved by reducing agents like vitamin C (ascorbic acid), which chemically converts ferric iron (Fe3+) into the soluble ferrous iron (Fe2+) state inside the digestive tract.

(a) 1 mark for iron-deficiency anaemia (accept anaemia).
(b) 2 marks (1 mark per symptom) for any of: fatigue/tiredness; pale skin/pallor; headaches; breathlessness; dizziness; lethargy; brittle nails; cold hands and feet.
(c) 2 marks: 1 mark for identifying vitamin C / ascorbic acid (or animal protein/meat); 1 mark for explaining that vitamin C chemically converts ferric iron to ferrous iron / enhances solubility and uptake in the gut.

(a) The egg white (albumen) contains ovalbumin, mucin, and globulin. The egg yolk contains vitellin and livetin.
(b) Convalescents (recovering from illness or surgery) require foods that support tissue repair and immune function without overloading the digestive tract. Eggs provide high biological value (HBV) proteins containing all essential amino acids, are soft and easy to digest, and are packed with vitamins A, D, and B-group, along with easily absorbable iron.

(a) 2 marks (1 mark per protein + correct location) for any of: ovalbumin / mucin / conalbumin in egg white; vitellin / livetin in egg yolk.
(b) 3 marks (1 mark per reason) for any of: HBV protein for rapid repair/healing of tissues; easily digested / puts minimal strain on the gut; rich in iron to restore red blood cells / boost energy; contains vitamins A/D/B-group for immune support/recovery; soft texture (easy to chew/swallow).

(a) Chemically, monounsaturated fatty acids contain a single carbon-to-carbon double bond (C=C) along the carbon chain. Because of this double bond, the chain is not fully saturated with hydrogen atoms and has a slight bend at the double bond site.
(b) Olive oil is famously rich in oleic acid (a monounsaturated fatty acid). Other rich plant sources include rapeseed/canola oil, peanut/groundnut oil, sesame oil, and avocado oil.

(a) 2 marks: 1 mark for stating it has only one double bond between carbon atoms; 1 mark for explaining that it can accept more hydrogen / is not fully saturated with hydrogen.
(b) 3 marks (1 mark per correct plant oil) for any of: olive oil, rapeseed/canola oil, peanut/groundnut oil, sesame oil, avocado oil.

(a)(i) The main proteins in egg white are ovalbumin (the most abundant) and mucin (which contributes to the viscosity/foam stability), along with conalbumin/ovotransferrin.
(ii) Whisking stretches and denatures the globular proteins, unfolding their polypeptide chains. The hydrophobic parts of the proteins orient toward the air bubbles, while the hydrophilic parts orient toward the water phase, forming a structural protective mesh that stabilizes the foam.
(b)(i) Lecithin is the natural emulsifier found in egg yolk.
(ii) Emulsifiers contain both polar (hydrophilic) and non-polar (hydrophobic) ends. The non-polar hydrophobic end embeds in the dispersed oil phase, while the polar hydrophilic end remains in the aqueous phase, reducing surface tension and preventing the dispersed oil droplets from grouping together.

a(i) [2 marks]
1 mark for each correct protein (e.g., ovalbumin, conalbumin/ovotransferrin, mucin, globulin).
a(ii) [3 marks]
1 mark for mentioning air incorporation/mechanical action.
1 mark for mentioning denaturation/unfolding of proteins.
1 mark for explaining that proteins form a film around air bubbles to trap them.
b(i) [1 mark]
Lecithin.
b(ii) [3 marks]
1 mark for stating lecithin has both hydrophilic and hydrophobic properties.
1 mark for stating the hydrophobic tail attaches to oil.
1 mark for stating the hydrophilic head attaches to water/acid, preventing separation.

(a)(i) Yeast requires warm temperatures (ideally 25°C-35°C), moisture (to activate), and a source of fermentable carbohydrates (sugar/starch) to act as food.
(ii) Anaerobic fermentation by yeast converts simple sugars (glucose) into carbon dioxide (which acts as the raising agent) and ethanol (alcohol, which mostly evaporates during baking).
(b) In the hot oven, gases expand, and yeast works intensely until the heat destroys the cells at 55°C. The gluten network stretches with the expanding gas until it coagulates/hardens at around 70°C-80°C, providing the firm crumb structure of the baked bread.

a(i) [3 marks]
1 mark for each correct condition: warmth/temperature, moisture/water, food/sugar (or starch/glucose).
a(ii) [2 marks]
1 mark for reactant (Glucose/Sugar).
1 mark for products (Carbon dioxide + Ethanol/Alcohol).
b [4 marks]
1 mark for mentioning rapid gas expansion / oven spring.
1 mark for stating yeast is destroyed/killed at ~55-60°C.
1 mark for explaining that gluten coagulates / sets to form structure at ~70-80°C.
1 mark for stating starch gelatinises (absorbs water).

(a)(i) Common plant-based starches include cereal grains (wheat, corn, rice) and root vegetables (arrowroot, tapioca, potato).
(ii) Gelatinisation occurs because heat breaks down the intermolecular bonds of starch granules, allowing water to enter. The granules swell until they eventually burst, releasing amylose molecules which form a network that traps water, thickening the sauce.
(b)(i) Syneresis (or weeping) is the reverse process of gelatinisation where the starch network contracts over time, forcing out the trapped water.
(ii) Continuous stirring prevents the starch from sinking and clumping together. Dispersing the starch in fat (as in a roux) or cold liquid first ensures uniform hydration.

a(i) [2 marks]
1 mark for each plant source (e.g., wheat, corn, potato, arrowroot, rice).
a(ii) [4 marks]
1 mark for stating starch grains absorb liquid at ~60°C.
1 mark for stating starch grains swell in size.
1 mark for explaining starch grains rupture/burst at ~80°C.
1 mark for stating that amylose is released and thickens the liquid/boils at 100°C.
b(i) [1 mark]
Liquid separates from a gel/shrinkage of gel.
b(ii) [2 marks]
1 mark each for any of: stir continuously, disperse starch in cold liquid/fat first, avoid freezing the cooked sauce.

(a)(i) Oxidative rancidity occurs primarily in unsaturated fats where oxygen attacks double bonds, producing aldehydes and ketones that taste bad.
(ii) Storage in opaque, airtight containers at cool temperatures reduces the rate of oxidation.
(b)(i) Shortening occurs because the fat barrier stops the formation of a cohesive gluten network. Gluten requires water to develop; by waterproofing the flour with fat, the pastry remains crumbly and tender instead of elastic and tough.
(ii) Harder fats like butter (for flavour) and lard (for optimal shortening power) are ideal.

a(i) [2 marks]
1 mark for stating it is a reaction with oxygen.
1 mark for mentioning the production of unpleasant odours/tastes/spoiled fat.
a(ii) [2 marks]
1 mark for each method (e.g., cool place/refrigerator, airtight container/cover, dark place/away from light).
b(i) [3 marks]
1 mark for explaining fat coats flour particles with a waterproof layer.
1 mark for stating it prevents flour absorbing water.
1 mark for explaining that gluten cannot develop/stretchy network cannot form, making it crumbly/short.
b(ii) [2 marks]
1 mark for each: butter, lard, margarine, block vegetable fat.

(a)(i) HTST (plate pasteurisation) uses a continuous flow system heating milk to 72°C for 15 seconds before immediate cooling. This kills pathogens like Mycobacterium tuberculosis.
(ii) Pasteurisation target is pathogen elimination. Spores survive, but the reduction of vegetative bacteria extends refrigerated shelf life to 10-14 days. The mild heat prevents denaturation of proteins and minimal loss of water-soluble B vitamins.
(b)(i) UHT temperatures (135°C-150°C) destroy heat-sensitive vitamins like thiamin, folate, and B12.
(ii) Sterile packaging allows ambient storage for months, offering convenience for emergency stocks and bulk transport.

a(i) [2 marks]
1 mark for heating to 72°C for 15 seconds.
1 mark for rapid cooling to under 10°C/5°C.
a(ii) [3 marks]
1 mark for stating it destroys pathogenic/harmful bacteria.
1 mark for stating it reduces the number of spoilage bacteria/spores.
1 mark for explaining that short time/mild heat preserves nutrients.
b(i) [2 marks]
1 mark for each vitamin (e.g., Vitamin C, Thiamin/B1, Vitamin B12).
b(ii) [2 marks]
1 mark for each advantage (e.g., unopened does not require refrigeration, very long shelf life, convenient for emergency storage).

### Nutritive Value and Structural Components of Eggs (Max 7 marks)

* **Proteins:** Eggs contain High Biological Value (HBV) protein, containing all essential amino acids. *Ovalbumin* is the main protein found in egg white, while *vitellin* is found in the yolk. These are essential for growth and repair.
* **Fats:** Present only in the yolk, in an easily digestible emulsified form. Contains both saturated fat and cholesterol, as well as essential fatty acids.
* **Vitamins:** Egg yolk is an excellent source of fat-soluble vitamins A (for vision and skin), D (for calcium absorption), and E (antioxidant). B-group vitamins (especially riboflavin, \(B_2\)) are present in both the white and the yolk.
* **Minerals:** Excellent source of iron (in the yolk, essential for haemoglobin formation), phosphorus, and calcium (mostly in the shell, but some in the yolk).
* **Water:** Egg white is high in water content (around 88%), while yolk contains about 50% water.
* **Lack of nutrients:** Eggs completely lack Vitamin C and dietary fibre (NSP).
* **Shell:** A porous protective outer layer composed of calcium carbonate, which allows gas exchange.
* **Membranes:** Double membrane inside the shell protecting the contents from bacterial contamination.
* **Chalazae:** Spiral bands of twisted albumen that anchor the yolk in the centre of the egg.
* **Air Space:** Found at the broad end of the egg between the membranes; grows larger as the egg loses moisture over time.

### Culinary Functions of Eggs in Food Preparation (Max 8 marks)

* **Aeration / Trapping Air:** When egg white is whisked, the protein denatures and stretches to trap air bubbles, forming a foam. Example: meringues, soufflés, Swiss rolls.
* **Binding:** As egg proteins heat up, they coagulate (set) and hold dry ingredients together. Example: rissoles, meatballs, fish cakes.
* **Coating:** Beaten egg is used to coat food, acting as an adhesive so breadcrumbs or flour stick. It coagulates during cooking to form a protective seal that prevents fat absorption. Example: fried fish, Scotch eggs.
* **Emulsification:** Egg yolk contains lecithin, a natural emulsifier that prevents immiscible liquids (like oil and water/vinegar) from separating. Example: mayonnaise, Hollandaise sauce.
* **Thickening:** Egg proteins coagulate and thicken liquid mixtures at temperatures between \(60^\circ\text{C}\) and \(70^\circ\text{C}\). Example: baked egg custard, sauces.
* **Glazing:** Egg wash (beaten egg or egg mixed with milk) brushed onto pastries caramelizes and shines when baked. Example: scones, sausage rolls, pies.
* **Enrichment:** Eggs increase the overall nutritional profile of a dish. Example: fresh pasta dough, enriched yeast dough (brioche).
* **Garnishing:** Hard-boiled eggs are sliced or wedged to add color and decorative appeal to dishes. Example: salads, nicoise salad.

Award 1 mark for each valid point up to a maximum of 15 marks.

**Nutritive Value and Structural Components (Max 7 marks):**
* HBV protein / ovalbumin / vitellin;
* Fat / cholesterol in yolk;
* Fat-soluble vitamins A / D / E in yolk;
* B-group vitamins / \(B_2\) in white/yolk;
* Minerals: Iron / calcium / phosphorus;
* High water content in white;
* Shell (protective, calcium carbonate);
* Inner/outer membranes (bacterial barrier);
* Chalazae (anchors yolk);
* Air space (enlarges with age);
* (Note: No Vitamin C or dietary fibre/NSP in eggs).

**Culinary Functions (Max 8 marks - 1 mark for function + explanation, 1 mark for example):**
* Aeration: Egg white traps air when whisked (e.g. meringues / soufflés / sponge cakes);
* Binding: Coagulation holds ingredients together (e.g. rissoles / fishcakes / burgers);
* Coating: Egg acts as adhesive for breadcrumbs, sealing food during frying (e.g. Scotch eggs / fried fish);
* Emulsification: Lecithin in yolk keeps oil and water combined (e.g. mayonnaise / Hollandaise);
* Thickening: Proteins coagulate to thicken liquids (e.g. custard / sauces);
* Glazing: Brushed egg shines and browns dough during baking (e.g. scones / pastry / buns);
* Enrichment: Increases nutrient value (e.g. fresh pasta / brioche);
* Garnishing: Adds colour and visual appeal (e.g. salads).